1. Field of the invention
The present invention relates to a semiconductor laser diode (laser diode hereinafter) that emits visible short wave rays in the blue to violet and also in the ultraviolet regions. Especially, the invention relates to a laser diode which requires a lower threshold current for oscillation.
2. Description of the Prior Art
A conventional laser diode disclosed in U.S. Pat. No. 5,247,533 comprises a gallium nitride group compound semiconductor satisfying the formula (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y N inclusive of 0.ltoreq.x.ltoreq.1 and 0.ltoreq.y.ltoreq.1, and an active layer not doped with any impurities. Consequently, the laser diode has a problem in that it requires high threshold current for oscillation.